NATO Secretary General Anders Fogh Rasmussen has offered condolences to Australia following the deaths of five Australian soldiers in Afghanistan.
In a statement on Twitter, Rasmussen described Australia as a "strong and steadfast" NATO partner.
Earlier, Australian Prime Minister Julia Gillard described the deaths as the "worst" single day of bloodshed for Australia in Afghanistan since the conflict began in late 2001.
The military said three Australian soldiers were killed and two wounded after a man in an Afghan army uniform opened fire at a base in Uruzgan province late on August 29.
The shooter escaped.
It was the latest in a series of recent "insider" attacks by men wearing Afghan security forces on foreign troops.
In a separate unrelated incident on August 30, two Australian soldiers died after their helicopter crashed while landing in Helmand province.
A crew member on board was wounded.
Australian Prime Minister Julia Gillard, who is at a Pacific nations' leaders forum in the Cook Islands, said she would be returning to Canberra.
Some 45 coalition troops, mostly Americans, have died in more than 30 such attacks this year.
NATO is training Afghan troops before handing over combat command to Afghan forces by mid-2013.
Insurgents 'Killed In South Afghanistan'
Elsewhere in Afghanistan, officials in the southeastern Afghan province of Paktika said Afghan troops have killed six insurgents.
Daulat Khan Zadran, Paktika provincial police chief, said his forces conducted the overnight operation in the remote Gul Rahman village of Khushamand district.
Zadran said that the six insurgents were killed in a police ambush.
He claimed that the insurgents were harassing the local population.
Paktika borders Pakistan's Waziristan region.
Afghan and NATO officials consider it a key infiltration route for Afghan insurgents and foreign Islamist militants based in Waziristan.
Based on reporting by AFP, AP, and dpa